The present invention relates to dental tools, and in particular to apparatus for retracting water from the water supply line of a dental tool when the tool has been deactivated.
The relatively cumbersome and complex valve assemblies traditionally used to control the flow of dental fluids to various dental tools are rapidly being replaced by smaller and more efficient diaphragm valves. An example of the use of such diaphragm control valves is illustrated in the patent to Austin, U.S. Pat. No. 3,638,310 which shows several discrete valve blocks mounted in series to form a dental tool control. A problem with such diaphragm valves and other dental control valves known in the art is that when a dental tool is deactivated, water will often continue to be discharged from the tool for a short period of time due to excess water in the water supply line running from the control valve to the tool. This excess water results from expansion of the water supply line when it is under pressure, and the excess water is discharged when the pressure is relieved. Water from the supply line may also be discharged when not desired by the siphon effect caused by operation of the turbine or chip air in the tool.
In order to solve this problem, control valves such as that illustrated by Austin incorporate an extra valve assembly which retracts a portion of the water from the water supply line to a given tool when that tool is deactivated. The extra valve assembly for water retraction ordinarily used in such control valves employs a balloon diaphragm to retract the water. This balloon diaphragm is operated by air at relatively high pressure, greater than the line pressure used to operate the dental tools. Hence, a separate high pressure line is required to operate the water retraction assembly.
The diaphragm control valves of the type illustrated in the patent to Austin use a plurality of discrete valves, one valve for each dental tool, with separate supply lines to each valve. The addition of an extra valve for water retraction with its own air pressure line does not sufficiently detract from the efficiency of the apparatus to render its use unacceptable. However, dental control valves have recently been developed wherein a plurality of dental tools are controlled from a single laminated control block, as illustrated in my copending patent application for DENTAL TOOL CONTROL ASSEMBLY, filed Apr. 13, 1973, Ser. No. 351,052, and herein incorporated by reference. The incorporation of an extra valve assembly as described above with its own air supply line for the sole purpose of water retraction would defeat the purpose and advantages of such a unitary control block to a large degree, and the use of such an extra valve with a unitary control valve is therefore undesirable.